Effect of internal cooling/heating coil on adsorption/regeneration of solid desiccant tray for controlling air humidity

Thermal performances of solid desiccant tray having internal cooling/heating coil for air humidity adsorption and desiccant regeneration are investigated. Three units of desiccant tray each of 48 cm × 48 cm cross‐sectional area and 2.5 cm thickness filled with silica gel are tested in a wind tunnel. For adsorption process, an air stream is flowing through the desiccant trays and the air humidity is captured by the silica gel. Approximately 10–40% of air humidity could be adsorbed more in case of the internal cooling. Besides, the outlet air temperature increases only slightly. In regeneration process, a hot air stream is used to repel the moisture in the silica gel. With the internal heating, the regeneration time is shorter compared with that without internal water heating. In addition, a correlation for calculating the adsorption/regeneration performance of the silica gel trays is developed and the results from the model agree well with the experimental data. Copyright © 2008 John Wiley & Sons, Ltd.     

Heat transfer model of slurry ice melting on external surface of helical coil

This research studies the heat transfer phenomenon of melting slurry ice on external surface of a copper helical coil. There is water flowing inside the tube coil and exchanging heat with the slurry ice. In this experiment, the coil diameters are 6.35 mm and 9.53 mm each of 4.2 m coil length. The mass flow rate of water in the helical coil is between 0.0149–0.0562 kg/s, while the inlet temperature of water is varied in the range of 23–27 °C. The slurry ice has 60% ice and 40% water by mass at the starting.     

Air-Side Performance Analysis of a Wire-on-Tube Heat Exchanger With an Oscillating Heat Pipe as an Extended Surface Under Natural Convection Conditions

This study investigates the performance of a wire-on-tube heat exchanger that uses an oscillating heat pipe as an extended surface under natural convection. The results have been compared with those of a conventional wire-on-tube unit. The heat exchanger exchanges heat between hot water flowing inside the tube, which is varied from 50 to 85°C, and the surrounding ambient air, which is kept constant at 25°C. The tested unit is installed in the horizontal and vertical directions, and the effects of tube diameter and tube and wire pitches on thermal performance are considered. The results show that the performance of the heat exchanger with an oscillating heat pipe is slightly higher than that of the conventional wire-on-tube heat exchanger. It was also found that the air-side performance of the heat exchanger is directly proportional to the tube diameter and tube and wire pitches. Moreover, when the heat exchanger is installed horizontally, its performance is approximately 15–20% higher than that of the unit in the vertical installation. A heat transfer model for evaluating the heat exchanger performance is also developed, and the results agree well with the experimental data.     

Performance Improvement of Thermosyphon Heat Exchangers by Using Two Kinds of Working Fluids

In this study, the concept of introducing two-fluid thermosyphons is examined. Calculations were performed for both low and high temperature ranges with parallel and counter-flow arrangements. For lower-temperature application, 125°C > T _hi > 75°C, use of ammonia in some rows and water in the rest of the thermosyphon can slightly improve the associated heat transfer performance for balanced counter-flow arrangement. However, for balanced parallel-flow arrangement in both lowand high-temperature applications, the concept of using two-fluid thermosyphons may not be feasible. The use of two-fluid thermosyphons is especially advantageous for high-temperature applications. For instance, in the range of 375°C > T _hi > 350°C, the two-fluid thermosyphons (Dowtherm A-water) shows a 15-99% increase of heat transfer performance relative to Dowtherm A alone.     

Performance analysis of a refrigeration cycle using a direct contact evaporator

This research work studies an ice thermal energy storage having an injection of R12 refrigerant into the water to exchange heat directly. The water temperature decreases to the freezing point and ice is formed. The ice is used for creating chilled water for an air-conditioning purpose. The system consists of a compressor, a condenser, an expansion valve and a direct contact evaporator. This system has a capacity of approximately 2 tons of refrigeration. The system simulation created from the mathematical model of each component has been carried out. It was found that the performance of the system depends on two factors, the compressor speed and the mass flow rate of the refrigerant. The suitable conditions are 8–10 rps for the compressor speed and 0.04–0.06 kgs⁻¹ for the mass flow rate. The coefficient of performance is about 3·4–3·6 which is higher than that of the conventional system. © 1998 John Wiley & Sons, Ltd.     

Use of oscillating heat pipe technique as extended surface in wire-on-tube heat exchanger for heat transfer enhancement

This paper presents the performance of a wire-on-tube heat exchanger of which the wire is an oscillating heat pipe. The experiments for this heat exchanger were performed in a wind tunnel by exchanging heat between hot water flowing inside the heat exchanger tubes and air stream flowing across the external surface. R123, methanol and acetone were selected as working fluids of the oscillating heat pipe. The inlet water temperature was varied from 45 to 85 °C while the inlet air temperature was kept constant at 25 °C.     

Performance analysis of solar water heater combined with heat pump using refrigerant mixture

In the research presented in this paper the thermal performance of a solar water heater combined with a heat pump is studied. A solar collector was modified from corrugated metal roofing with a copper tube attached beneath. The performance of the solar water heater was tested, and models for the collector efficiency and storage tank were developed and used for the evaluation of their performance when combined with a heat pump system.     

Thermal analysis of slurry ice production system using direct contact heat transfer of carbon dioxide and water mixture

This research studies the heat transfer characteristic during ice formation of a direct contact heat transfer between carbon dioxide and water mixture. This research is divided into two parts. For the first part, the low temperature carbon dioxide, between − 15 and − 60 °C, is injected into water initially at 28 °C and exchanges heat directly. The flow rate of carbon dioxide is varied between 0.003 and 0.017 kg/s while the volume of water is between 1 and 3 L. From the experiment, it is found that the effectiveness of the direct contact heat transfer between the carbon dioxide and the water is closed to 100%. Moreover, the lumped model is found to be used for predicting the temperature of water and the mass of ice formation quite well.     

Comparison of Conventional Flat-Plate Solar Collector and Solar Boosted Heat Pump Using Unglazed Collector for Hot Water Production in Small Slaughterhouse

This study presents simulated results of solar water heating systems in a small slaughterhouse using two techniques. The first one is a normal solar water heating system using a flat-plate solar collector and the second one uses a solar-boosted heat pump system having a corrugated metal sheet roof as a solar collector. The number of solar collector units is between 1 and 5, and the volume of water in a storage tank is 300–1200 L. The heat pump in this work uses refrigerant mixture R22:R124:R152a of 20%:57%:23% as the working fluid. The weather conditions of Chiang Mai, Thailand, are taken as the input data. In the case of the normal solar water heating system, the shortest payback periods for 300, 600, 900, and 1200 L water are 3.63, 3.12, 2.95, and 2.82 yr, respectively. The suitable number of collectors for 300 L water is 1 unit with 600–900 L water storage; 2 units of collectors is suitable in the case of 1200 L water, and 3 units of collectors gives the shortest payback period. However, in the case of a solar heat pump system, the suitable payback periods for 300, 600, 900, and 1200 L water are 2.74, 1.79, 1.83, and 1.88 yr, respectively. In our case, 1 unit of this collector gives the shortest payback period.     

Effect of electric field on heat transfer performance of automobile radiator at low frontal air velocity

The effect of electric field on the performance of automobile radiator is investigated in this work. In this experiment, a louvered fin and flat tube automobile radiator was mounted in a wind tunnel and there was heat exchange between a hot water stream circulating inside the tube and a cold air stream flowing through the external surface. The electric field was supplied on the airside of the heat exchanger and its supply voltage was adjusted from 0 kV to 12 kV.From the experiment, it was found that the unit with electric field pronounced better heat transfer rate, especially at low frontal velocity of air. The correlations for predicting the air-side heat transfer coefficient of the automobile radiator, with and without electric field, at low frontal air velocity were also developed and the predicted results agreed very well with the experimental data.